Malignant gliomas are among the most fatal cancers. Microglia (MG) and macrophages (MP) represent a significant component of the brain response to malignant brain tumors. Although the exact contribution of these cells to the tumor microenvironment is unclear, our preliminary studies indicate that MG/MP immune function in brain tumor models is suppressed by tumor cells. This suppression most likely occurs through the activation of Stat3 in MG/MP. We hypothesize that inhibition of Stat3 in MG/MP can enhance their pro-inflammatory function and could lead to tumor abrogation. In vivo modification of MG/MP function is difficult because these cells are resistant to transfection with standard viral and nonviral gene transfer methods. However, the inherent phagocytic property of MG/MP can be exploited for nanoparticle-mediated drug delivery into these cells. Due to their low toxicity in comparison to viral systems, nanoparticle systems have recently generated significant excitement in the field of therapeutics. One example is carbon nanotubes (CNT), which are unique nanostructures with remarkable electronic and mechanical properties. The ability of CNTs to carry small inhibitory RNA (siRNA) into MP could be exploited for MG/MP modulation and stimulation in brain tumor models. To develop a novel brain tumor immunotherapy based on MG/MP activation, we propose to study the efficacy of CNTs for siRNA delivery into MG/MP in glioma models. In the first Aim of the project, we will optimize the efficacy of CNTs for siRNA delivery into MG in vitro. More specifically, we will evaluate the following parameters: CNT toxicity, CNT-mediated siRNA delivery and gene silencing and CNT-mediated MG activation through Stat3 inhibition. The second Aim of the project will examine the efficacy of CNTs for siRNA delivery into MG/MP in brain tumor models. After optimizing siRNA delivery conditions in vitro, we will characterize CNS response and duration of gene silencing in experimental brain tumors following CNT-mediated siRNA delivery. Finally, these results will be used to test whether CNT-mediated Stat3-siRNA delivery results in MG/MP activation and enhancement of antitumor immunity in a murine glioma model. Overall, these studies will investigate a novel immunotherapy approach based on CNT-mediated siRNA delivery that can be used for MG/MP activation in brain tumors and ultimately be translated for human applications. PUBLIC HEALTH RELEVANCE: With a two-year survival of less than 20%, malignant gliomas are among the most fatal cancers in humans. Although immunotherapy is being studied as a possible treatment for malignant brain tumors, the immunosuppressive glioma environment has limited the efficacy of this approach. We believe that direct activation of the innate immune system using a carbon nanotube (CNT) delivery system may help overcome this local immunosuppression and ultimately lead to the development of a novel immunotherapeutic approach for the treatment of malignant brain tumors. Furthermore, modification of brain macrophages with CNT may have therapeutic relevance to other CNS disease processes, such as trauma and stroke, where brain macrophages play a key role in their pathogenesis.